Plate glass

Abstract

To create a plate-like glass with high scratch resistance.SOLUTION: A plate-like glass has a fracture toughness K1C of 0.9 or more and, preferably, includes a compressive stress layer by ion exchange on its surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to plate glass, and more particularly to cover glass suitable for touch panel displays such as mobile phones, digital cameras, PDAs (portable terminals), and the like.

Background Art

[0002] Mobile phones, digital cameras, PDAs (portable terminals), etc. are becoming increasingly popular. For these applications, ion-exchanged strengthened glass is used as the cover glass for touch panel displays (see Patent Document 1 and Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0005] Cover glass, especially the cover glass used in smartphones, is often used outdoors, so it is prone to hard scratches, that is, scratches with large width and depth. As a result, starting from the scratches, the cover glass is likely to be damaged. Therefore, it is important to improve the scratch resistance of the cover glass.

[0006] As a method for enhancing scratch resistance, increasing the hardness of the cover glass has been considered. Specifically, since conventional glass has a significantly lower hardness than silica (sand) that is abundant on the ground, it has the property of being easily scratched due to silica. Therefore, it is considered that increasing the hardness of the cover glass makes it difficult for the surface to be scratched. However, when attempting to increase the hardness of the cover glass, the high-temperature viscosity of the glass increases, significantly reducing its meltability and formability. Furthermore, the balance of the glass composition is disrupted, making it easier for devitrified products to occur during molding. As a result, it becomes difficult to obtain good products.

[0007] In addition, it is known that forming a hard thin film on the glass surface increases the hardness of the cover glass (see, for example, Patent Document 2). However, when forming a hard thin film on the glass surface, there is a risk that the transparency of the cover glass may decrease or that the cover glass may warp due to film stress.

[0008] Note that sapphire seems to be suitable for the cover member because of its high hardness. However, it is difficult to mass-produce large-sized plate-like bodies of sapphire.

[0009] The present invention has been made in view of the above circumstances, and its technical problem is to create a plate-like glass with high scratch resistance.

Means for Solving the Problem

[0010] As a result of various studies by the present inventors, it has been found that the fracture toughness K of the glass is closely related to the size of the scratch, and it has been found that the above technical problem can be solved by increasing the fracture toughness K of the plate-like glass to be higher than a predetermined value, and the present invention is proposed. That is, the plate-like glass of the present invention is characterized in that the fracture toughness K is 0.9 MPa·m or more. Here, "fracture toughness K" 1C is closely related to the size of the scratch, and it has been found that the above technical problem can be solved by increasing the fracture toughness K of the plate-like glass to be higher than a predetermined value, and the present invention is proposed. That is, the plate-like glass of the present invention is characterized in that the fracture toughness K is 0.9 MPa·m or more. Here, "fracture toughness K" 1C is higher than a predetermined value, and the present invention is proposed. That is, the plate-like glass of the present invention is characterized in that the fracture toughness K 1C is 0.9 MPa·m 0.5 or more. Here, "fracture toughness K" 1C」 is measured using the single-edge-precracked-beam method (SEPB method) based on JIS R1607 "Test Method for Fracture Toughness of Fine Ceramics". The SEPB method measures the maximum load until the test piece breaks by a three-point bending fracture test of the pre-cracked test piece, and calculates the plane strain fracture toughness K from the maximum load, pre-crack length, test piece dimensions, and bending fulcrum distance. 1C This is the method. The measured value of the fracture toughness K of each glass is the average value of five measurements. 1C

[0011] As described above, the plate glass of the present invention is characterized in that the fracture toughness K 1C is 0.9 or more. In this way, it becomes difficult for surface scratches to occur, and even when a hard scratch is made, the width and depth of the scratch can be reduced. FIG. 1 is a graph showing the relationship between the fracture toughness K 1C and the width of the scratch, and FIG. 2 is a graph showing the relationship between the fracture toughness K 1C and the depth of the scratch. As is clear from FIGS. 1 and 2, when the fracture toughness is greater than 0.9 MPa·m 0.5 , it can be seen that the width and depth of the scratch are significantly reduced.

[0012] Further, in the plate glass of the present invention, the content of MgO in the glass composition is preferably more than 10 mol%.

[0013] Further, the plate glass of the present invention preferably contains, in mol%, 30 to 70% of SiO2, 5 to 30% of Al2O3, 0 to 15% of B2O3, 0 to 7% of Li2O, 0 to 20% of Na2O, 0 to 10% of K2O, and more than 10 to 50% of MgO as the glass composition.

[0014] Further, in the plate glass of the present invention, the content of P2O5 in the glass composition is preferably 1 mol% or more.

[0015] In addition, the plate glass of the present invention preferably satisfies the relationship of [MgO] / [Al2O3] ≧ 1.0. Here, "[MgO] / [Al2O3]" refers to the value obtained by dividing the molar% content of MgO by the molar% content of Al2O3.

[0016] In addition, the plate glass of the present invention preferably satisfies the relationship of [MgO] / [Na2O] ≧ 1.0. Here, "[MgO] / [Na2O]" refers to the value obtained by dividing the molar% content of MgO by the molar% content of Na2O.

[0017] In addition, the plate glass of the present invention preferably has a Li2O content in the glass composition of more than 0.1 mol%.

[0018] In addition, the plate glass of the present invention preferably contains, as a glass composition, in mol%, 60 to 80% of SiO2, 1 to 30% of Al2O3, 0 to 15% of B2O3, more than 0.1% to 30% of Li2O, 0 to 20% of Na2O, 0 to 10% of K2O, and 0 to 20% of MgO.

[0019] In addition, the plate glass of the present invention preferably contains 0.1 mol% or more of Y2O3 in the glass composition.

[0020] In addition, the plate glass of the present invention preferably has a Young's modulus of 90 GPa or more. Here, the "Young's modulus" can be measured by a well-known resonance method.

[0021] In addition, the plate glass of the present invention preferably has a compressive stress layer formed by ion exchange on the surface.

[0022] In addition, the plate glass of the present invention preferably has a compressive stress value of the compressive stress layer of 300 MPa or more and a stress depth of 15 μm or more. Here, the "compressive stress value" and the "stress depth" refer to the values calculated by a surface stress meter (surface stress meter FSM-6000LE manufactured by Origen).

[0023] Also, the plate glass of the present invention preferably has a CT limit greater than 65 MPa. Here, the "CT limit" refers to the internal tensile stress value at which the number of fragments with a size of 0.1 mm or more becomes 100 pieces / inch 2 and indicates the internal tensile stress value at which the number of fragments becomes 100 pieces / inch 2 The "internal tensile stress value at which the number of fragments becomes 100 pieces / inch 2 is obtained by first performing an indentation test using a diamond chip on a surface plate and collecting the fragment number data at CTcv values (two points) where the number of fragments causing delayed fracture exceeds 100 pieces / inch 2 and the fragment number data at CTcv values (two points) when the number of fragments is less than 100 pieces / inch

[0024] Next, after drawing an exponential approximation curve from the fragment number data at a total of four CTcv values, the CTcv value at which the number of fragments becomes 100 is calculated as the CT limit from the approximation curve. The CTcv value can be obtained by the software FsmV of the surface stress meter FSM-6000LE manufactured by Orihara Seisakusho. Also, the fragment number data at each point is the average value of three measurements.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0026] In the plate glass of the present invention, the fracture toughness K 1C is 0.9 MPa·m 0.5 or more, preferably 1.0 MPa·m 0.5 or more, and particularly preferably 1.1 to 3.5 MPa·m 0.5That is. In particular, the fracture toughness K in the state where ion exchange treatment has not been performed 1C is preferably 0.9 MPa·m 0.5 or more, more preferably 1.0 MPa·m 0.5 or more, and particularly preferably 1.1 to 3.5 MPa·m 0.5 That is. The fracture toughness K 1C If it is too small, the surface of the cover glass is likely to be scratched. Even when a hard scratch is made, the width and depth of the scratch are likely to increase. Furthermore, after ion exchange treatment, the non-fragility (CT limit) increases.

[0027] In the plate glass of the present invention, the Young's modulus is preferably 90 GPa or more, 100 GPa or more, particularly 105 to 150 GPa. If the Young's modulus is low, the cover glass is likely to bend when the plate thickness is thin.

[0028] The plate glass of the present invention preferably has a glass composition included in the following glass composition range A and / or glass composition range B.

[0029] Glass composition range A contains, as a glass composition, in mol%, 30 to 70% of SiO2, 5 to 30% of Al2O3, 0 to 15% of B2O3, 0 to 7% of Li2O, 0 to 20% of Na2O, 0 to 10% of K2O, and more than 10 to 50% of MgO. The reasons for limiting the content ranges of the respective components are shown below. In the description of the content ranges of the respective components, the % indication refers to mol% unless otherwise specified.

[0030] SiO2 is a component that forms the glass network. The content of SiO2 is preferably 30 to 70%, 32 to 61%, 33 to 55%, less than 34 to 50%, particularly 35 to 45%. If the content of SiO2 is too small, it becomes difficult to vitrify, and the thermal expansion coefficient becomes too high, making it easy for the thermal shock resistance to decrease. On the other hand, if the content of SiO2 is too large, the meltability and formability are likely to decrease, and the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of the surrounding materials.

[0031] Al2O3 is the fracture toughness K1C is a component that enhances it, and also a component that enhances ion exchange performance, strain point, and Young's modulus. If the content of Al2O3 is too low, the fracture toughness K 1C tends to decrease, and there is a risk that the ion exchange performance cannot be fully exerted. Therefore, the content of Al2O3 is preferably 5% or more, 8% or more, 10% or more, 12% or more, 14% or more, particularly 15% or more. On the other hand, if the content of Al2O3 is too high, the high-temperature viscosity increases, and the meltability and formability tend to decrease. In addition, devitrification crystals are likely to precipitate in the glass, making it difficult to form into a plate shape by the overflow down-draw method or the like. In particular, when using an alumina-based refractory as the formed body refractory and forming it into a plate shape by the overflow down-draw method, devitrification crystals of spinel are likely to precipitate at the interface with the alumina-based refractory. Furthermore, the acid resistance also decreases, making it difficult to apply to the acid treatment process. Therefore, the content of Al2O3 is preferably 30% or less, 25% or less, particularly 21% or less.

[0032] B2O3 is a component that decreases the high-temperature viscosity and density, stabilizes the glass, and decreases the liquidus temperature. However, if the content of B2O3 is too high, the Young's modulus tends to decrease. Therefore, the content of B2O3 is preferably 0 to 15%, 0.1 to 10%, 1 to 7%, particularly 2 to 5%.

[0033] Li2O is an ion exchange component, and also a component that decreases the high-temperature viscosity, enhances the meltability and formability, and significantly enhances the fracture toughness K 1C On the other hand, if the content of Li2O is too high, the devitrification resistance tends to decrease, and there is a risk of eluting into the ion exchange solution during the ion exchange treatment, deteriorating the ion exchange solution. Therefore, the content of Li2O is preferably 0 to 7%, 0 to 3%, 0 to 1.5%, less than 0 to 1%, 0 to 0.5%, 0 to 0.3%, less than 0 to 0.1%, particularly 0.01 to 0.05%.

[0034] Na2O is an ion-exchange component, a component that increases the compressive stress value of the compressive stress layer, and also a component that reduces the high-temperature viscosity to enhance the meltability and formability. Further, Na2O is a component that enhances the devitrification resistance, and in particular, a component that suppresses devitrification occurring in the reaction with alumina-based refractories. If the content of Na2O is too high, it becomes difficult to enjoy the above effects. On the other hand, if the content of Na2O is too low, the high-temperature viscosity increases, the meltability and formability decrease, or the compressive stress value of the compressive stress layer tends to decrease. Therefore, the content of Na2O is preferably 0 to 20%, 1 to 17%, particularly 5 to 15%.

[0035] K2O is a component that reduces the high-temperature viscosity to enhance the meltability and formability. However, among the alkali metal oxides, it is a component that reduces the compressive stress value of the compressive stress layer and increases the stress depth, so it is not advantageous from the viewpoint of increasing the compressive stress value. Therefore, the content of K2O is preferably 0 to 10%, 0 to 5%, particularly less than 0 to 1%.

[0036] MgO is a component that significantly increases the fracture toughness K 1C and also a component that enhances the meltability and formability. However, if the content of MgO is too high, the devitrification resistance tends to decrease, and it becomes difficult to suppress devitrification occurring in the reaction with alumina-based refractories. Therefore, the content of MgO is preferably more than 10 to 50%, 15 to 45%, 20 to 42%, 25 to 40%, particularly 30 to 35%.

[0037] P2O5 is a component that enhances the ion-exchange performance and in particular a component that increases the stress depth. However, if the content of P2O5 is too high, the glass is likely to phase-separate or the water resistance tends to decrease. Therefore, the content of P2O5 is preferably 0 to 20%, 0.5 to 19%, 1 to 18%, particularly 2 to 15%.

[0038] The total content of Al2O3 and MgO is preferably more than 20 to 55%, 25 to 50%, 30 to 45%, 32 to 42%, particularly 35 to 40%. If the total content of Al2O3 and MgO is too low, the fracture toughness K 1C tends to decrease.

[0039] [MgO] / [Al2O3] is preferably 0.9 or more, 1.2 or more, particularly 1.5 to 3.5. If [MgO] / [Al2O3] is too small, it becomes difficult to increase the fracture toughness K 1C while reducing the meltability and formability.

[0040] [MgO] / [Na2O] is preferably 1.0 or more, 1.5 or more, particularly 2.0 to 20. If [MgO] / [Na2O] is too small, the fracture toughness K 1C tends to decrease.

[0041] The glass composition range B contains, as a glass composition, in mol%, 60 to 80% of SiO2, 1 to 30% of Al2O3, 0 to 15% of B2O3, more than 0.1% to 30% of Li2O, 0 to 20% of Na2O, 0 to 10% of K2O, and 0 to 20% of MgO. The reasons for limiting the content ranges of the respective components are shown below. In the description of the content ranges of the respective components, the % indication refers to mol% unless otherwise specified.

[0042] SiO2 is a component that forms the glass network. The content of SiO2 is preferably 60 to 80%, 63 to 78%, particularly 65 to 75%. If the content of SiO2 is too small, it becomes difficult to vitrify, and the thermal expansion coefficient becomes too high, making the thermal shock resistance tend to decrease. On the other hand, if the content of SiO2 is too large, the meltability and formability tend to decrease, and the thermal expansion coefficient becomes too low, making it difficult to match the thermal expansion coefficient of the surrounding materials.

[0043] Al2O3 is a component that increases the fracture toughness K 1C and is also a component that increases the ion exchange performance, strain point, and Young's modulus. If the content of Al2O3 is too small, the fracture toughness K 1CIt is likely to decrease, and there is a risk that the ion exchange performance cannot be fully exerted. Therefore, the content of Al2O3 is preferably 1% or more, 5% or more, 8% or more, 10% or more, particularly 12% or more. On the other hand, if the content of Al2O3 is too high, the high-temperature viscosity will increase, and the meltability and formability are likely to decrease. In addition, devitrification crystals are likely to precipitate in the glass, making it difficult to form into a plate shape by the overflow down-draw method or the like. In particular, when using an alumina-based refractory as the shaped body refractory and forming it into a plate shape by the overflow down-draw method, devitrification crystals of spinel are likely to precipitate at the interface with the alumina-based refractory. Furthermore, the acid resistance also decreases, making it difficult to apply to the acid treatment process. Therefore, the content of Al2O3 is preferably 30% or less, 25% or less, particularly 21% or less.

[0044] B2O3 is a component that reduces the high-temperature viscosity and density, stabilizes the glass, and reduces the liquidus temperature. However, if the content of B2O3 is too high, the Young's modulus is likely to decrease. Therefore, the content of B2O3 is preferably 0 to 15%, 0 to 10%, 0 to 5%, particularly 0 to 1%.

[0045] Li2O is an ion exchange component, and is also a component that reduces the high-temperature viscosity, enhances the meltability and formability, and significantly enhances the fracture toughness K 1C On the other hand, if the content of Li2O is too high, the devitrification resistance is likely to decrease, and there is a risk of eluting into the ion exchange solution during the ion exchange treatment, deteriorating the ion exchange solution. Therefore, the content of Li2O is preferably more than 0.1% to 30%, 0.1 to 20%, 0.1 to 18%, 3 to 15%, particularly 5 to 12%.

[0046] Na2O is an ion-exchange component, a component that increases the compressive stress value of the compressive stress layer, and also a component that reduces the high-temperature viscosity to enhance the meltability and formability. Further, Na2O is a component that enhances the devitrification resistance, and in particular, a component that suppresses devitrification caused by the reaction with alumina-based refractories. If the content of Na2O is too high, it becomes difficult to enjoy the above effects. On the other hand, if the content of Na2O is too low, the high-temperature viscosity increases, the meltability and formability decrease, or the compressive stress value of the compressive stress layer tends to decrease. Therefore, the content of Na2O is preferably 0 to 20%, less than 0 to 10%, particularly 0.1 to 5%.

[0047] K2O is a component that reduces the high-temperature viscosity to enhance the meltability and formability. However, among alkali metal oxides, it is a component that reduces the compressive stress value of the compressive stress layer and increases the stress depth, so it is not advantageous from the viewpoint of increasing the compressive stress value. Therefore, the content of K2O is preferably 0 to 10%, 0 to 5%, particularly less than 0 to 1%.

[0048] MgO is a component that significantly increases the fracture toughness K 1C and also a component that enhances the meltability and formability. However, if the content of MgO is too high, the devitrification resistance tends to decrease, and it becomes difficult to suppress devitrification caused by the reaction with alumina-based refractories. Therefore, the content of MgO is preferably 0 to 20%, more preferably 0 to 20%, 0 to 10%, 0 to 8%, 0.1 to 5%, particularly 1 to 3%.

[0049] P2O5 is a component that enhances the ion-exchange performance, and in particular, a component that increases the stress depth. However, if the content of P2O5 is too high, the glass tends to phase-separate or the water resistance tends to decrease. Therefore, the content of P2O5 is preferably 0 to 10%, 0 to 3%, 0 to 1%, particularly 0 to 0.5%.

[0050] In the glass composition ranges A and B, in addition to the above components, for example, the following components may be introduced.

[0051] CaO is a component that can significantly lower the high-temperature viscosity and enhance the meltability and formability without accompanying a decrease in devitrification resistance compared to other components. However, if the CaO content is too high, the ion exchange performance may deteriorate, and the ion exchange solution is prone to degradation during the ion exchange process. Therefore, the CaO content is preferably 0 - 6%, 0 - 5%, 0 - 4%, 0 - 3.5%, 0 - 3%, 0 - 2%, 0 - 1%, particularly 0 - 0.5%.

[0052] SrO and BaO are components that can lower the high-temperature viscosity, enhance the meltability and formability, and increase the strain point and Young's modulus. However, if their contents are too high, in addition to the fracture toughness K 1C being prone to decrease, the density and coefficient of thermal expansion increase, and the glass is prone to devitrification. Therefore, the preferred contents of SrO and BaO are 0 - 5%, 0 - 2%, 0 - 1.5%, 0 - 1%, 0 - 0.5%, 0 - 0.1%, particularly less than 0 - 0.1% respectively.

[0053] ZnO is a component that can lower the high-temperature viscosity without reducing the low-temperature viscosity. It is also a component that can enhance the ion exchange performance, especially with a significant effect on increasing the compressive stress value. However, if the ZnO content is too high, the glass tends to phase-separate, the devitrification resistance decreases, the density increases, and the stress depth becomes smaller. Therefore, the ZnO content is preferably 0 - 3%, 0 - 2%, 0 - 1%, particularly less than 0 - 1%.

[0054] ZrO2 is a component that can increase the Young's modulus and also enhance the viscosity and strain point near the liquid-phase viscosity. However, if its content is too high, there is a risk of significant decrease in devitrification resistance. Therefore, the ZrO2 content is 0 - 10%, 0 - 5%, 0 - 3%, preferably 0 - 1%, particularly 0 - 0.1%.

[0055] TiO2 is a component that can enhance the ion exchange performance and Young's modulus, and also lower the high-temperature viscosity. However, if its content is too high, the transparency and devitrification resistance are prone to decrease. Therefore, the TiO2 content is preferably 0 - 10%, 0 - 4.5%, less than 0 - 1%, 0 - 0.5%, particularly 0 - 0.3%.

[0056] SnO2 is a component that enhances the ion exchange performance. However, if its content is too high, the devitrification resistance tends to decrease. Therefore, the content of SnO2 is preferably 0 to 3%, 0.01 to 3%, 0.05 to 3%, 0.1 to 3%, particularly 0.2 to 3%.

[0057] As a clarifying agent, one or more selected from the group of Cl, SO3, CeO2 (preferably the group of Cl, SO3) may be added in an amount of 0.001 to 1%.

[0058] Also, as a clarifying agent, Sb2O3 may be added in an amount of 0.001 to 1%. Depending on the high-temperature viscosity that changes according to the glass composition, an effective clarifying agent can be added.

[0059] The preferred content of Fe2O3 is less than 1000 ppm (less than 0.1%), less than 800 ppm, less than 600 ppm, less than 400 ppm, particularly less than 300 ppm. Furthermore, after regulating the content of Fe2O3 within the above range, it is preferable to regulate the molar ratio SnO2 / (Fe2O3 + SnO2) to 0.8 or more, 0.9 or more, particularly 0.95 or more. In this way, the total light transmittance at a wavelength of 400 to 770 nm and a thickness of 1 mm is likely to be improved.

[0060] Y2O3 is a component that enhances the fracture toughness K 1C However, Y2O3 has a high cost of the raw material itself, and when added in a large amount, the devitrification resistance tends to decrease. Therefore, the content of Y2O3 is preferably 0 to 15%, 0.1 to 12%, 1 to 10%, 1.5 to 8%, particularly 2 to 6%.

[0061] Gd2O3, Nb2O5, La2O3, Ta2O5 are components that enhance the fracture toughness K 1C However, Gd2O3, Nb2O5, La2O3, Ta2O5 have a high cost of the raw material itself, and when added in a large amount, the devitrification resistance tends to decrease. The total content and individual contents of Gd2O3, Nb2O5, La2O3, Ta2O5 are preferably 0 to 15%, 0 to 10%, 0 to 5%, particularly 0 to 3%.

[0062] From an environmental consideration perspective, the sheet glass of the present invention preferably contains substantially no As2O3, PbO, F, etc. as the glass composition. Also, from an environmental consideration perspective, it is also preferable to substantially contain no Bi2O3. "Substantially does not contain ~" means that although no explicit components are actively added as glass components, the addition at the impurity level is allowed. Specifically, it refers to the case where the content of the explicit component is less than 0.05%.

[0063] In addition to the above characteristics, the sheet glass of the present invention preferably has the following characteristics.

[0064] The density is preferably 3.50 g / cm 3 Hereinafter, 3.25 g / cm 3 Hereinafter, 3.00 g / cm 3 Hereinafter, 2.90 g / cm 3 Hereinafter, 2.80 g / cm 3 Hereinafter, 2.70 g / cm 3 Hereinafter, 2.60 g / cm 3 Hereinafter, 2.55 g / cm 3 Hereinafter, 2.50 g / cm 3 Hereinafter, 2.49 g / cm 3 Hereinafter, particularly 2.40 to 2.47 g / cm 3 That is. The lower the density, the more the cover glass can be lightened. Note that if the content of SiO2, B2O3, and P2O5 in the glass composition is increased, or the content of alkali metal oxides, alkaline earth metal oxides, ZnO, ZrO2, and TiO2 is decreased, the density is likely to decrease.

[0065] The temperature at 10 2.5 dPa·s of the high-temperature viscosity is preferably 1660 °C or lower, less than 1640 °C, 1630 °C or lower, 1620 °C or lower. The lower limit is not particularly limited, but 1600 °C to 1400 °C is preferable. If the temperature at 10 2.5 dPa·s of the high-temperature viscosity is too high, the meltability and formability will decrease, and it will be difficult to form the molten glass into a sheet shape.

[0066] The liquid-phase viscosity is preferably 10 3.0above dPa·s, 10 3.5 above dPa·s, 10 4.0 above dPa·s, 10 4.4 above dPa·s, 10 4.8 above dPa·s, 10 5.0 above dPa·s, 10 5.3 above dPa·s, particularly 10 5.5 It is above dPa·s. Note that the higher the liquid-phase viscosity, the better the devitrification resistance, and it becomes difficult for devitrified products to occur during forming. Here, the "liquid-phase viscosity" refers to the value measured by the platinum ball pulling-up method for the viscosity at the liquid-phase temperature. The "liquid-phase temperature" refers to the highest temperature at which devitrification (devitrified products) is observed inside the glass by microscopic observation after putting glass powder that has passed through a standard sieve of 30 mesh (500 μm) and remained on a 50 mesh (300 μm) sieve into a platinum boat and holding it in a temperature gradient furnace for 24 hours and then taking out the platinum boat.

[0067] In the plate-shaped glass of the present invention, the plate thickness is preferably 2.0 mm or less, 1.5 mm or less, 1.3 mm or less, 1.1 mm or less, 1.0 mm or less, particularly 0.9 mm or less. The smaller the plate thickness, the lighter the cover glass can be. On the other hand, if the plate thickness is too thin, it becomes difficult to obtain the desired mechanical strength. Therefore, the plate thickness is preferably 0.3 mm or more, 0.4 mm or more, 0.5 mm or more, 0.6 mm or more, particularly 0.7 mm or more.

[0068] The method for manufacturing the plate-shaped glass of the present invention is, for example, as follows. First, glass raw materials prepared to have a desired glass composition are charged into a continuous melting furnace, heated and melted at 1400 to 1700 °C, clarified, and then, after supplying the molten glass to a forming device, it is preferably formed into a plate shape and cooled. As a method of cutting the formed plate shape into a predetermined size, a well-known method can be adopted.

[0069] As a method for forming molten glass into a plate shape, it is preferable to adopt the overflow down-draw method. The overflow down-draw method is a method capable of producing a large amount of high-quality plate glass. Here, the "overflow down-draw method" is a method in which molten glass overflows from both sides of a shaped refractory, and the overflowed molten glass is joined at the lower end of the shaped refractory while being drawn downward and formed into a plate shape. In the overflow down-draw method, the surface that should become the surface of the plate glass does not contact the surface of the shaped refractory and is formed into a plate shape in a free surface state. Therefore, it is possible to inexpensively manufacture a plate glass with a good surface quality without polishing.

[0070] In addition to the overflow down-draw method, various forming methods can be adopted. For example, forming methods such as the float method, the down-draw method (slot down-draw method, redraw method, etc.), the roll-out method, and the press method can be adopted.

[0071] The plate glass of the present invention may or may not be subjected to ion exchange treatment. However, when ion exchange treatment is performed, a compressive stress layer is formed on the surface, so the fracture toughness K 1C can be increased. The conditions for the ion exchange treatment are not particularly limited, and optimal conditions may be selected in consideration of the viscosity characteristics, thickness, internal tensile stress, dimensional change, etc. of the glass. In particular, when K ions in a KNO3 molten salt are ion-exchanged with Na components in the glass, a compressive stress layer can be efficiently formed. During the ion exchange treatment, the temperature of the ion exchange solution is preferably 400 to 450 °C, and the ion exchange time is preferably 2 to 6 hours. In this way, a compressive stress layer can be efficiently formed on the surface. Further, Na ions in a NaNO3 molten salt or a mixed molten salt of KNO3 and NaNO3 may be ion-exchanged with Li components in the glass.

[0072] The plate glass of the present invention preferably has a compressive stress layer formed by ion exchange on the surface, and the compressive stress value of the compressive stress layer is preferably 300 MPa or more, 400 MPa or more, 500 MPa or more, 600 MPa or more, and particularly preferably 700 MPa or more. The greater the compressive stress value, the greater the fracture toughness K 1Cit increases. On the other hand, if an extremely large compressive stress is formed on the surface, the internal tensile stress becomes extremely high, and there is a risk that the dimensional change before and after the ion exchange treatment becomes large. Therefore, the compressive stress value of the compressive stress layer is preferably 1800 MPa or less, 1650 MPa or less, particularly 1500 MPa or less. Note that if the ion exchange time is shortened or the temperature of the ion exchange solution is lowered, the compressive stress value tends to increase.

[0073] The stress depth of the compressive stress layer is preferably 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, particularly 35 μm or more. The greater the stress depth, the smaller the variation in mechanical strength. On the other hand, the greater the stress depth, the higher the internal tensile stress becomes, and there is a risk that the dimensional change before and after the ion exchange treatment becomes large. Furthermore, if the stress depth is too large, the compressive stress value tends to decrease. Therefore, the stress depth is preferably 60 μm or less, 50 μm or less, particularly 45 μm or less. Note that if the ion exchange time is lengthened or the temperature of the ion exchange solution is raised, the stress depth tends to increase.

[0074] The internal tensile stress value is preferably 150 MPa or less, 120 MPa or less, 100 MPa or less, 80 MPa or less, 70 MPa or less, particularly 60 MPa or less. If the internal tensile stress value is too high, the cover glass is likely to self-destruct due to hard scratches. On the other hand, if the internal tensile stress value is too low, it becomes difficult to ensure the mechanical strength of the cover glass. The internal tensile stress value is preferably 15 MPa or more, 25 MPa or more, 35 MPa or more, particularly 40 MPa or more. Note that the internal tensile stress value is a value calculated by (compressive stress value × stress depth) / (plate thickness - 2 × stress depth), and can be measured by the software FsmV of the surface stress meter FSM-6000LE manufactured by Orihara Seisakusho.

[0075] The CT limit is preferably 65 MPa or more, 70 MPa or more, 80 MPa or more, 90 MPa or more, particularly 100 MPa to 300 MPa. Also, the CT limit in terms of a plate thickness of 0.5 mm is preferably 65 MPa or more, 70 MPa or more, 80 MPa or more, 90 MPa or more, particularly 100 MPa to 300 MPa. If the CT limit is too low, it becomes difficult to increase the stress depth, and it becomes difficult to ensure the mechanical strength of the cover glass.

[0076] The plate-shaped glass of the present invention is preferably amorphous glass, but may be crystallized by heat treatment or the like to be crystallized glass.

Examples

[0077] Hereinafter, the present invention will be described based on examples. Note that the following examples are merely illustrative. The present invention is not limited to the following examples at all.

[0078] Table 1 shows the glass compositions and glass properties of the examples (Sample Nos. 1 to 14) of the present invention.

[0079]

Table 1

[0080] Each sample in the table was prepared as follows. First, glass raw materials were formulated to have the glass compositions in the table, and melted at 1550 °C for 21 hours using a platinum pot. Subsequently, the obtained molten glass was poured onto a carbon plate, formed into a flat plate shape, and then gradually cooled in a slow cooling furnace. For the obtained plate-shaped glass, after optically polishing the surface so that the plate thickness became 0.8 mm, various properties were evaluated.

[0081] The Young's modulus E is a value measured by a well-known resonance method.

[0082] Fracture toughness K 1CIt is measured by the SEPB method based on JIS R1607 "Test Method for Fracture Toughness of Fine Ceramics". The fracture toughness value of each glass was determined from the average value of five points.

[0083] As is clear from Table 1, Samples No. 1 to 14 are considered to have high scratch resistance because the fracture toughness K 1C is 0.9 or more.

Example

[0084] Table 2 shows the glass compositions and glass properties of the example (Sample No. 15) and the comparative example (Sample No. 16) of the present invention.

[0085]

Table 2

[0086] Each sample in the table was prepared as follows. First, glass raw materials were formulated to obtain the glass compositions in the table, and melted at 1450 °C for 8 hours using a platinum pot. Subsequently, the obtained molten glass was poured onto a carbon plate, formed into a flat plate shape, and then gradually cooled in a slow cooling furnace. For the obtained plate-shaped glass, the surface was optically polished to various plate thicknesses, and then various properties were evaluated.

[0087] The Young's modulus E and the fracture toughness K 1C were determined by the above method.

[0088] The density is a value measured by the well-known Archimedes method.

[0089] The coefficient of thermal expansion α is a value measured with a dilatometer in the temperature range of 30 to 380 °C.

[0090] The photoelastic constant is a value calculated with a photoelastic constant measuring device manufactured by Union Opto.

[0091] The refractive index nd was measured by the V-block method. nd is the refractive index at the d-line.

[0092] Next, for Sample Nos. 15 and 16, ion exchange treatment was carried out by immersing each sample in a KNO3 molten salt at 430 to 480 °C for 4 to 8 hours, and tempered glass having various CTcv values was obtained at each plate thickness. The CTcv value was obtained from the CTcv value of the software FsmV of the surface stress meter FSM-6000LE of Orihara Manufacturing Co., Ltd. based on the above photoelastic constant and refractive index nd.

[0093] Subsequently, ion exchange treatment was carried out under various conditions at various plate thicknesses of Sample Nos. 15 and 16 to produce tempered glass with different stress states. Subsequently, an indenter test using a diamond chip was performed on a surface plate, and the number of fragments with a size of 0.1 mm or more when causing delayed fracture was 100 pieces / inch 2 exceeding the CTcv value (two points), and the fragment number data at the CTcv value (two points) when the number of fragments was less than 100 pieces / inch 2 were collected. The fragment number data at each point is the average value of three measurements. Further, after drawing an exponential approximation curve from the fragment number data at a total of four CTcv values, the CTcv value at which the number of fragments becomes 100 was calculated as the CT limit from the approximation curve. The results are shown in Fig. 3. In Fig. 3, the dotted line is a graph showing the relationship between the plate thickness of Sample No. 15 and the CT limit, and the solid line is a graph showing the relationship between the plate thickness of Sample No. 16 and the CT limit.

[0094] As can be seen from Fig. 3, since Sample No. 15 had a high fracture toughness K 1C , the CT limit was higher than that of Sample No. 16.

Claims

Claim 1 As a glass composition, in mol%, SiO ２ 30 to less than 50%, Al ２ O ３ 8 to 16%, B ２ O ３ 0 to 1%, MgO 30 to 50%, BaO 0 to 5%, CaO 0 to 1%, TiO ２ 0 to less than 1%, satisfying the relationship of [MgO] / [Na₂O] ≥ 1.0, and the fracture toughness K １Ｃ is 0.9 MPa·m ０．５ or more, characterized by a plate-shaped glass. Claim 2 P in the glass composition ２ O ５ The sheet glass according to claim 1, characterized in that the content of is 1 mol% or more. Claim 3 [MgO] / [Al ２ O ３ ≥0.9, characterized in that it is the plate glass according to claim 1 or 2. Claim 4 [[MgO]] / [[Na ２ The plate glass according to any one of claims 1 to 3, characterized by satisfying the relationship of [[MgO]] / [[Na ２ O]] ≧ 1.

5. Claim 5 Li in the glass composition ２ The sheet glass according to any one of claims 1 to 4, characterized in that the content of O is more than 0.1 mol%. Claim 6 Y in the glass composition ２ O ３ The sheet glass according to any one of claims 1 to 5, characterized in that it contains 0.1 mol% or more of Claim 7 The plate-shaped glass according to any one of Claims 1 to 6, characterized in that the Young's modulus is 90 GPa or more. Claim 8 The plate-shaped glass according to any one of Claims 1 to 7, characterized in that it has a compressive stress layer formed by ion exchange on the surface. Claim 9 The plate-shaped glass according to Claim 8, characterized in that the compressive stress value of the compressive stress layer is 300 MPa or more and the stress depth is 15 μm or more. Claim 10 The plate-shaped glass according to any one of Claims 1 to 9, characterized in that it is used as a cover glass for a touch panel display.

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